1. Field of the Invention
This invention relates to nonaqueous dyeing of synthetic polymers.
2. Description of the Prior Art
Solvent dyeing procedures, that is, dyeing procedures wherein an organic solvent is employed at least partially in place of water in conventional aqueous procedures such as aqueous exhaust dyeing procedures, represent a commercially significant means of dyeing synthetic polymers with disperse dyes. This means of dyeing is significant not only in batch processes but also in continuous processes. Continuous processes generally involve use of lesser volumes of liquids than batch processes; moreover, in continuous processes the disperse dye generally is applied to the substrate by a padding or printing operation. Continuous solvent dyeing processes may provide improved appearance in the dyed product and elimination of an after dyeing scour treatment and their use may preclude water damage to certain water sensitive fabrics such as stretch goods and knit fabrics. Byland et al. in the Journal of the American Association of Textile Chemists and Colorists, Vol. 3, No. 10, October 1971, pages 210-215, describe four solvent methods, all basically padding procedures, for application of a disperse dye: (1) application of a solvent-dye solution, (2) application of a solubilized dye composition, (3) application of a solvent-dye dispersion and (4) application of a solvent-aqueous dye emulsion. These four application methods can be employed in combination with, basically, three methods for dye fixation: (a) heating with saturated solvent vapor, (b) heating with hot air or steam and (c) heating with superheated solvent vapor.
Following is a representation of various possible application and fixation processes:
I. aqueous padding, drying and saturated vapor fixation by (a). PA1 Ii. solvent padding by any of 1-4, drying and saturated vapor fixing by (a) or hot air (Thermosol) fixing by (b). PA1 Iii. solvent padding by any of 1-4, no drying and saturated vapor fixing by (a) or superheated vapor fixing by (c).
A process similar to Process I is known in the trade as the "Vapocol" process. A process similar to Process II with saturated vapor fixing is described in U.S. Pat. No. 3,667,898. A process similar to Process III with superheated vapor fixing is known in the trade as the "Solvofix" process. Such processes also are described by Byland et al., supra, and in Belgian Pat. No. 760,243.
Every liquid in a closed system, that is, wherein vapors are not lost from the system, exists in equilibrium with its vapors; the pressure of the vapor is called the vapor pressure. The vapor pressure of a pure liquid is primarily, but not entirely, a function of temperature. Expressed mathematically, P.sub.v = ke .sup..sup.-.sup..delta.H/RT wherein P.sub.v is the vapor pressure, k is a constant characteristic of the liquid, e is the natural logarithmic Naperian base, .DELTA.H is the heat of vaporization, R is the universal gas constant and T is the absolute temperature. For any liquid, once k and .DELTA.H are determined P.sub.v can be determined from T and vice versa. If the vapor pressure P.sub.v is held constant and the vapor is heated to a higher temperature T' (that is, T' is larger than T in the above equation), the vapor is said to be superheated. A superheated vapor cannot exist in equilibrium with a liquid phase; it must first be cooled to its saturated vapor temperature T. Thus, an advantage in the use of superheated trichloroethylene or tetrachloroethylene vapor, as disclosed by Byland et al., supra, is that the vapor can be used to heat the dyed textile without forming a liquid phase provided the vapor is not allowed to cool to its saturated vapor temperature. In contrast, a saturated vapor can only heat the textile by condensing to liquid.
U.S. Pat. No. 3,762,872 teaches the exposure of a cool moving web of fabric having unfixed dye thereon in a first zone to the saturated vapors of a solvent, whereby it is taught that liquid acting as the dyeing medium is condensed thereon. Immediately thereafter the fabric is exposed to superheated vapors which evaporate the condensed solvent and fixes the dye. Tetrachloro- and trichloroethylene are exemplified; various chlorocarabons, chlorofluoro-carbons and fluorocarbons such as perfluoroheptane, perfluorohexane, and perfluoro(2,2,4-trimethyl)pentane are taught to be operable.
U.S. Pat. No. 3,667,898 discloses generically the use of numerous solvents for dyeing, including tri- and tetrachloroethylene and C.sub.1-4, chlorinated and fluorinated, saturated aliphatic hydrocarbons. German Published Application No. 2,002,286 discloses the pad application of dyes from fluorinated solvents, for example, CFCl.sub.3, C.sub.2 F.sub.3 Cl.sub.3, C.sub.2 F.sub.4 Cl.sub.2, with fixation being effected with hot air, with superheated steam or with vapors or organic solvents (undefined), the vapors being at a temperature of 105.degree.-130.degree.C. This publication also discloses that fixation can be effected by contacting the padded material with molten metal (also disclosed in U.S. Pat. No. 3,634,014 and German Published Application No. 1,963,015), paraffin waxes, oxalkylation products of alcohols or fatty acids and eutectic salt melts at 100.degree.-220.degree.C. British Pat. No. 1,130,354 discloses fixing of dyes by means of a hot oil bath.
With the exception of the solvent vapor and hot air fixation methods, all the aforesaid methods generally leave residues on the dyed fabric and, hence, are disadvantageous in that the residues must be removed. Similarly, although tetrachloroethylene solvent vapors may lead to more rapid fixation than hot air fixation, since tetrachloroethylene may be retained in the fibers, a removal step may be required.